Effects of Cyano-Substituents on the Molecular Packing Structures of Conjugated Polymers for Bulk-Heterojunction Solar Cells

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• 作者：Hyojung Cha ; Hyoung Nam Kim ; Tae Kyu An ; Moon Sung Kang ; Soon-Ki Kwon ; Yun-Hi Kim ; Chan Eon Park
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2014
• 出版时间：September 24, 2014
• 年：2014
• 卷：6
• 期：18
• 页码：15774-15782
• 全文大小：538K
• ISSN：1944-8252

文摘

The molecular packing structures of two conjugated polymers based on alkoxy naphthalene, one with cyano-substituents and one without, have been investigated to determine the effects of electron-withdrawing cyano-groups on the performance of bulk-heterojunction solar cells. The substituted cyano-groups facilitate the self-assembly of the polymer chains, and the cyano-substituted polymer:PC₇₁BM blend exhibits enhanced exciton dissociation to PC₇₁BM. Moreover, the electron-withdrawing cyano-groups lower the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels of the conjugated polymer, which leads to a higher open circuit voltage (V_OC) and a lower energy loss during electron transfer from the donor to the acceptor. A bulk-heterojunction device fabricated with the cyano-substituted polymer:PC₇₁BM blend has a higher V_OC (0.89 V), a higher fill factor (FF) (51.4%), and a lower short circuit current (J_SC) (7.4 mA/cm²) than that of the noncyano-substituted polymer:PC₇₁BM blend under AM 1.5G illumination with an intensity of 100 mW cm^鈥?. Thus, the cyano-substitution of conjugated polymers may be an effective strategy for optimizing the domain size and crystallinity of the polymer:PC₇₁BM blend, and for increasing V_OC by tuning the HOMO and LUMO energy levels of the conjugated polymer.

Keywords:

electron-withdrawing cyano-groups; alkoxy naphthalene derivative; morphology control; conjugated polymer; phase separation; organic photovoltaics